Ink jet printing systems mark a printable medium by propelling droplets of ink onto the medium. Although a number of variations exist in the types of ink jet printing systems that are in use, the two main types of ink jet printing systems are Drop-On-Demand (DOD) printing systems and continuous ejection printing systems. DOD printing systems utilize heating elements or piezoelectric elements within ink ejection nozzles to propel ink on demand onto the medium. Continuous ejection printing systems utilize a continuous stream of ink and electrostatic fields to control the placement of the ink onto the medium.
In some cases, it may be desirable to apply a clear protectant to the ink features that have been marked to the medium. For example, the protectant may be used with water-soluble inks to prevent the ink from smearing or otherwise being affected by water. Applying the protectant is performed after the inked images are applied to the medium. For example, the protectant may be applied over the inked portions of the medium at a location in the print path that is downstream of the ink marking process.
The protectant is a consumable resource in a printing system and an expense in the printing process that is factored into the costs associated with the printing process. Typically the protectant is applied to the entire page or sheet of a job. However, applying the protectant in this manner can be wasteful, since inked features on the medium rarely encompass the entire page or sheet on the medium.